Apparatus and method for providing dual output signals in a telemetry transmitter

Abstract: Telemetry transmitting apparatus and a method are provided for reception and transmission of electrocardiogram (EKG) waveforms from a plurality of electrodes coupled to the body of a medical patient (10). A receiving facility of the apparatus receives a plurality of analog signals representing the EKG waveforms. An output signal representing the EKG waveforms is formed and transmitted, via a wireless coupling (50), to a telemetry receiver (20). An analog output (118) port is provided on the telemetry transmitting apparatus (100). The analog output port is also coupled to the receiving facility. A plurality of output signals representing the EKG waveforms is provided to the analog output port of the telemetry transmitting apparatus (100). The analog output port may be coupled to buffers at the input terminals of the apparatus. Alternatively, the output port may receive signals from the amplifier in the telemetry transmitter (100) that are gain adjusted to emulate the unprocessed voltage signals of the EKG electrodes.

Description: FIELD OF THE INVENTION The present invention relates to apparatus and methods for distributing data from a medical patient by way of a telemetry transmitting device. BACKGROUND OF THE INVENTION Telemetry transmitters provide a convenient means for remotely monitoring EKG signals from a medical patient. The telemetry transmitter is connected to the patient by electrodes and wires. The telemetry transmitter includes terminals for receiving the EKG signals from the wires, and a wireless transmitter that is typically a radio frequency (RF) link. Additional circuitry may be provided in the transmitter device for amplifying, filtering and multiplexing the received EKG signals. The transmitter sends the EKG signals to a telemetry receiver, which is typically in a central station. It is often desirable to monitor the EKG signals locally. For example, a doctor or nurse may wish to review the EKG while making his or her rounds. In some Telemetry transmitters, such as the model 1481T Telemetry transmitter manufactured by the Siemens Corporation, a display is provided for locally monitoring the EKG signals. This provides convenience, but increases the cost of the telemetry transmitter. An alternative method that allows local monitoring is to place a telemetry receiver in the patient's room and connect the telemetry receiver to a monitor, as is done at the central station. While convenient, this is also quite expensive. U.S. Patent No. 3,882,277 to DePedro et al. describes such a telemetry system. A telemetry receiver is placed in the patient's room, and the receiver is connected to a modem for transmission over a conventional telephone system. If the hospital has an EKG monitor available (for example, a mobile transport monitor), the EKG electrodes that are attached to the patient could be disconnected from the telemetry transmitter and reconnected to the transport monitor for in-room monitoring. This method is cost effective, but is inconvenient, because the patient's EKG signal is not received at the central station while the EKG electrodes are connected to the transport monitor. This method also requires that the caregiver perform four steps including: (1) disconnecting the electrodes from the telemetry transmitter; (2) connecting the electrodes to the transport monitor; (3) disconnecting the electrodes from the transport monitor, when local monitoring is completed; and (4) reconnecting the electrodes to the telemetry transmitter. Performing these steps takes up the caregiver's valuable time. Another problem associated with the method described above could occur while monitoring the quality of the electrode contacts. The quality of the EKG waveform is affected by the quality of the electrode contact to the skin, so viewing the EKG waveform from the bedside monitor via the telemetry transmitter allows evaluation of the electrode contact in the patient's room. Using the method described in the previous paragraph, the electrode contact may be disturbed while performing steps (3) and (4). The caregiver would not immediately become aware of this problem because he or she would no longer be viewing the waveform on the transport monitor. The discrepancy would not be detected until someone viewed the waveform back at the central station. At that point, it would be necessary to dispatch another person back to the patient's room to fix the electrode contact. A convenient, low cost apparatus for locally monitoring the output of an EKG telemetry transmitter is desired. SUMMARY OF THE INVENTION The present invention is embodied in a patient carried portable telemetry transmitting apparatus and a method for reception and transmission of electrocardiogram (EKG) waveforms. The waveforms are received from a plurality of electrodes coupled to the body of a medical patient. A receiving portion of the apparatus receives a plurality of analog signals representing the EKG waveforms. A first output signal representing the EKG waveforms is formed and transmitted, via a wireless coupling, from a first output port of the telemetry apparatus to a remotely located telemetry receiver. A second output port is also provided on the telemetry transmitting apparatus. The second output port is also coupled to the receiving portion of the apparatus. A second output signal also representing the EKG waveforms is provided to the second output port of the telemetry transmitting apparatus simultaneously with the wireless transmission of the first output signal from the first output port. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a block diagram of an exemplary system according to the invention. FIG. 2 is a block diagram of an exemplary embodiment of the telemetry transmitter shown in FIG. 1. FIG. 3 is a block diagram of a second embodiment of the telemetry transmitter shown in FIG. 1. FIG. 4 is a block diagram of the decoder/attenuator circuit shown in FIG. 3. DETAILED DESCRIPTION OF THE INVENTION FIG. 1 is a block diagram of an exemplary system including a telemetry transmitting apparatus 100 according to the invention. The telemetry transmitting apparatus 100 receives a plurality of analog signals representing the patient's condition, which may be, for example electrocardiogram (EKG) waveforms from a plurality of electrodes 120a-e coupled to the body of a medical patient 10. The transmitter provides means for forming and transmitting an output signal 50 representing the EKG waveforms, via a wireless coupling to a telemetry receiver 20. The telemetry receiver 20 may be of a conventional type, and may be coupled to a central station 40 for monitoring the patient's condition remotely. In accordance with the invention, the telemetry transmitter 118 also includes an analog output port 118, which provides a plurality of analog output signals representing the EKG waveforms. An electrical cable 34 may be used to connect the analog output port 118 of the telemetry transmitting apparatus 100 to the input port 32 of a monitor 30 in the patient's room. Monitor 30 may be any patient monitor capable of receiving EKG electrodes. For example, monitor 30 may be a conventional transport monitor, such as the SIRECUST 630 transport monitor, manufactured by the Siemens corporation. Using the analog output port 118, a medical caregiver can easily connect a monitor 30, to the telemetry transmitter 100 without the need to disconnect the electrodes 120a-e from transmitter 100. The process of connecting the transmitter 100 to the monitor 30 only involves the single step of connecting the cable 34 to the output port 118 and the input port 32. Similarly, disconnecting monitor 30 is performed in a single step. There is no interruption in transmitting signal 50 to the telemetry receiver 20 for remote monitoring during any of the periods when monitor 30 is being connected, when the patient's EKG is viewed locally, or when the monitor 30 is being disconnected. The EKG signals may be monitored locally, on monitor 30, and remotely, on monitor 40, at the same time. Another benefit of the invention is that the caregiver can verify the quality of the EKG waveform that is transmitted by the telemetry transmitter 100, without disturbing any existing connections. There is no need to disturb the electrodes to perform this evaluation. Cable 34 is connected to port 118 of the telemetry transmitter 100 to start local monitoring; and the cable 34 is unplugged from the port 118 when local monitoring is completed. FIGS. 2-4 show two exemplary embodiments of a telemetry transmitter 100 and 200 in accordance with the invention. FIG. 2 is a block diagram of an exemplary embodiment of the telemetry transmitting apparatus 100 shown in FIG. 1. Transmitter 100 provides reception and wireless transmission of electrocardiogram (EKG) waveforms. The waveform signals are received from a plurality of electrodes LA, LL, RA, C and RL (shown in FIG. 1) coupled to the body of a medical patient by electrode wires 120a-e. The electrodes are coupled to the left arm (LA), left leg (LL), right arm (RA), chest (C) and right leg (RL) of the patient 10. The EKG signals are received by transmitter 100 at a plurality of input terminals 111a-e. A plurality of buffers 112a-e are coupled to the input terminals 111a-e. Each buffer 112a-e receives a respective analog signal from a respective EKG electrode LA, LL, RA, C and RL. The terminals 111a-e and buffers 112a-e provide a means for receiving the plurality of analog signals representing the EKG waveforms. Each buffer 112a-e is an amplifier that has unity gain and unity feedback gain, with high input impedance and low output impedance. The buffers 112a-e hold the EKG data so that it may be provided to the EKG amplifier 102 and the analog output port 118. Buffers 112a-e are connected to output port 118 by a plurality of electrical couplings 116a-e. Other elements of the telemetry transmitter 100 may be the same components used in conventional telemetry transmitters. For example, EKG amplifier 102 includes an amplifier/combiner circuit (also referred to herein as amplifier) 122 for boosting the EKG voltage signals, and for combining the input voltage signals received from buffers 112a-e into three EKG lead signals. In the exemplary embodiment, the gain of amplifier 122 is 500. The amplifier circuit 122 forms the three leads from the five input voltage signals. The three leads are designated I, II, and V, which are the standard designations used in the field. Lead I is formed by the differential voltage between the left arm electrode LA and the right arm electrode RA, according to equation 1. I = LA - RA Lead II is formed by the differential voltage between the left leg electrode LL and the right arm electrode RA. II = LL - RA Lead V is formed by equation (3). V = C - (LA + RA + LL) / 3 where: C, LA, RA and LL designate the signals returned by the respective chest, left arm, right arm and left leg electrodes. The amplifier 102 also may also include a filter 124 for removing artifacts such as high-frequency noise (out of the frequency band of the EKG signal) from the EKG signal. The wireless transmitting circuitry 104, 106 and 108 may include conventional transmitting devices, coupled to the receiving circuitry 111a-e, 112a-e and 102, which form and transmit an output signal 50, representing the EKG waveforms, via a wireless coupling. In the exemplary telemetry transmitter 100, multiplexer 104 combines the EKG lead I, II and V signals into a single analog signal 105 that may be converted to digital format in analog to digital (A/D) converter 106. It is contemplated that the multiplexer 104 may combine the signals I, II and V using time-division multiplexing techniques or frequency division multiplexing techniques. The digital signal 107 is then frequency modulated in R/F modem 108, to format the data for transmission. The R/F modem 108 may include, for example, frequency shift keying (FSK) or quadrature amplitude modulation (QAM) circuitry. The output signal of the exemplary modem 108 is ready for transmission by an antenna 110. Using the apparatus of FIG. 2, the signals received at the analog output port 118 are the same as those input to EKG amplifier 102. FIG. 3 is a block diagram of a second exemplary embodiment of a telemetry transmitter 200 in accordance with the invention. Elements that are common between the two embodiments (102, 104, 106, 108, 110, 111a-e, 118, and 128a-e) have the same reference numerals as the corresponding elements in FIG. 2, for ease of identification. The description of these common elements is not repeated, for brevity. As is apparent from the drawing, analog output port 118 does not receive unconditioned signals directly from the input terminals 111a-e, as is the case in the embodiment of FIG. 2. Instead, the EKG lead signals I, II and V from leads 226a-c are provided to a combination decoder/attenuator device 220 that separates the three signals into five analog output signals, 128a-e. The decoder/attenuator 220 decodes each one of the amplified signals I, II and V, and attenuates the resulting individual signals to form a plurality of individual attenuated signals 128a-e that are substantially equal in magnitude to the respective analog signal LA, LL, RA, C and RL from which the amplified signals I, II and V are formed. In the embodiment of FIG. 3, there may be very small differences between the values of output signals 128a-e and the actual EKG voltages, because the artifacts filtered out by filter 124 are not restored within decoder/attenuator 220. FIG. 4 shows an exemplary embodiment of a circuit to perform the functions of decoder/attenuator 220. In the exemplary embodiment, the voltage of the right arm electrode RA is held at a reference potential (e.g., ground). With RA set to zero, equations (1) through (3) may be rewritten to separate out the left arm left leg and chest components as follows: LA = I LL = II C = V + (I + II) / 3 Additionally, all of the signals are reduced in magnitude by a constant factor that is equal to the gain of amplifier 102 (shown in FIG. 3). In the exemplary embodiment, EKG amplifier 102 has a gain of 500, so the decoder/attenuator 220 reduces all of the voltage signals by a factor of 0.002. The exemplary decoder/attenuator 220 is a voltage divider circuit. Although any number of circuits may be designed to perform the functions described above, the voltage divider provides a particularly inexpensive solution for achieving the desired gain adjustment and performing the arithmetic operations defined by equations (4) through (6). The left arm LA voltage is produced at node N1, between resistors R1 and R2. This portion of the voltage divider circuit implements equation (4), and performs the gain adjustment. In the exemplary embodiment, the desired gain is 0.002, so the ratio of R2/R1 is 0.002. Exemplary resistances are R1 = 100,000 Ohms, and R2 = 200 Ohms. The left leg LL voltage is produced at node N2, between resistors R3 and R4. This portion of the voltage divider circuit implements equation (5), and performs the gain adjustment. In the exemplary embodiment, the desired gain is 0.002, so the ratio of R4/R3 is 0.002. Exemplary resistances are R3 = 100,000 Ohms, and R4 = 200 Ohms. The Chest voltage is produced at node N3, between resistor R8 and the resistors R5, R6 and R7. This portion of the voltage divider circuit implements equation (6), and performs the gain adjustment. In the exemplary embodiment, the desired gain is 0.002, so the ratio of R8/R5 is 0.002, and R6/R8 = R7/R8 = 1500 . Exemplary resistances are R5 = 100,000 Ohms, R6 = R7 = 300,000 Ohms and R8 = 200 Ohms. It is understood by one of ordinary skill in the art that the use of a voltage divider to perform these arithmetic functions is most accurate and effective when there is a high gain in amplifier 102, so that the resistors R1, R3, R5, R6 and R7 are all much larger than R2, R4 and R8. In the exemplary embodiment, there are more than two orders of magnitude between the larger resistors and the smaller resistors, which is sufficient to accurately perform the attenuation function. It is also understood by one of ordinary skill in the art that any device coupled to receive one of the five signals LA, LL, RA, C and RL described has a high input impedance so that the device does not change the resistance ratios. It is further understood that many other circuits or devices could perform these functions, although the cost is likely to be higher. For example, attenuators containing active devices could be used to perform the gain adjustment. Furthermore, the choice of which EKG electrodes are used as the reference potential may be varied. In the exemplary embodiment, the right arm RA and right leg electrodes RL are considered to be ground. It would also be possible to use the left arm and left leg as ground. Although the invention has been described in terms of its applicability to EKG telemetry transmitters, it is understood that the invention may be practiced in telemetry transmitters that transmit other forms of medical patient data (e.g., EEG, blood pressure or temperature). It is understood by one skilled in the art that many variations of the embodiments described herein are contemplated. While the invention has been described in terms of exemplary embodiments, it is contemplated that it may be practiced as outlined above.

Claims: A portable patient monitoring apparatus of the type carried by a medical patient and having as its primary function the continuous reception and then wireless transmission to a remote patient monitoring device of medical data acquired from the patient, comprising: receiving circuitry(112a-e,102) adapted for being coupled to said patient for continuously receiving a plurality of analog signals representing in real-time a sensed physiological condition of the patient; wireless transmitting circuitry(104-110), including a signal processor and a wireless signal transmitter, coupled to the receiving circuitry for forming a first output signal representing the patient's sensed condition and applying said first output signal to a first output port(110) for transmitting said first output signal via a wireless transmission to a remote monitoring device(20,40) which is physically separate from said portable patient monitor apparatus(100), CHARACTERIZED IN THAT : said portable patient apparatus has a secondary function of also providing the sensed medical data to a second output port (118) of the portable patient monitoring apparatus (100) for facilitating local monitoring of the medical data, said second function being carried out by: a second output port (118) included as part of the portable patient monitoring apparatus (100); and output circuitry (128 a-e, 220) coupled to the receiving circuitry for providing a second output signal that also represents the patient's sensed condition, to the second output port(118) simultaneously with the wireless transmission of said first output signal to the remote monitoring device. Apparatus in accordance with claim 1, CHARACTERIZED IN THAT : said second output signal includes an analog EKG signal, and wherein the receiving circuitry includes EKG amplifying means (100) responsive to the analog EKG signal for developing an amplified EKG signal. Apparatus in accordance with claim 2, CHARACTERIZED IN THAT : the EKG amplifier (102) amplifies respective ones of a plurality of analog EKG signals by a predetermined factor to form a plurality of amplified signals (I,II,V); the wireless transmitting circuitry includes a radio frequency modulator(108) coupled to receive the amplified signals and to provide the first output signal; and the output circuitry includes means (220) for attenuating each one of the amplified signals by the predetermined factor to produce respective attenuated signals and for providing the attenuated signals at the second output port (118). Apparatus in accordance with claim 3, CHARACTERIZED IN THAT : the receiving circuitry includes means (122) for combining the plurality of amplified signals so that each combined signal represents a respectively different EKG lead signal; and the attenuating means (220) includes: means for decoding the amplified signals representing the EKG lead signals to produce a plurality of individual signals that represent the respective EKG signals, and means for attenuating the individual signals to form a plurality of EKG signals as said second output signal. Apparatus in accordance with claim 4, CHARACTERIZED IN THAT : the means for decoding and means for attenuating comprise a voltage divider circuit (R1-R8). Apparatus in accordance with claim 1, CHARACTERIZED IN THAT : the receiving circuitry includes a plurality of buffers (111 a-e), each buffer receiving one of the plurality of respective analog signals acquired from the patient; and the output circuitry includes means (128 a-e)for coupling the buffers to the second output port(118). Apparatus in accordance with claim 6, CHARACTERIZED IN THAT : the receiving circuitry includes an amplifier and filter (122,124) coupled to the buffers, the amplifier and filter amplifying and filtering each respective one of the plurality of analog signals. A method for operating a telemetry transmitter of the type carried by a medical patient and having as a primary function the reception of medical data acquired from a plurality of sensor devices coupled to a medical patient, and for providing via wireless transmission from a first output port (110), a signal to a remotely located display device for displaying the sensed medical data, wherein: said portable patient apparatus has a secondary function of also providing the medical data to a second output port (118) of the telemetry transmitter for facilitating transfer of the medical data to a local display device, the method comprising the steps of: (a) continuously receiving (via 120 a-e) from the sensor devices a plurality of analog signals representing in real-time a sensed physiological condition of the patient, the receiving being performed by the telemetry transmitter (100); (b) forming (via 102-108) a first output signal representing the medical data and transmitting said first output signal to said remotely located display device (20,40) via a wireless transmission(110) from a first output port (110), which remotely located display device is physically separate from said telemetry transmitter; and (c) forming and transmitting (via 128 a-e,220) a second output signal representative of the analog signals recited in step (a) to said second output port (118) of the telemetry transmitter (100), for use by the local display device (30) located proximate to the telemetry transmitter (100), simultaneously with the transmission of said first output signal to the remotely located display device (20,40) via said wireless transmission. A method in accordance with claim 8, CHARACTERIZED IN THAT : the sensor devices are EKG electrodes, step (a) includes the step of receiving a plurality of analog signals representing EKG signals; step (b) includes the step of forming and transmitting an output signal representing the EKG signals; and step (c) includes the step of forming and transmitting a plurality of analog output signals representing the EKG signals. A method in accordance with claim 9, further CHARACTERIZED BY the step of: (d) using a cable for coupling the second output port (118) of the telemetry transmitting apparatus (100) to the local display device (30), for locally displaying the EKG signals. A method in accordance with claim 9, CHARACTERIZED IN THAT step (b) includes the steps of: (1) amplifying the plurality of analog signals to form a plurality of amplified signals, (2) combining the plurality of the amplified signals to form a plurality of EKG lead signals, (3) multiplexing the plurality of EKG lead signals to form a single signal, and (4) modulating a radio frequency carrier with the single signal; and further CHARACTERIZED BY the step of: (f) transmitting the modulated signal from the telemetry transmitter (100) to said remotely located display device (20,40) via the wireless transmission. A method in accordance with claim 11, CHARACTERIZED IN THAT between steps (1) and (2), is the step of: (1a) filtering the plurality of amplified signals to attenuate signal components having frequencies outside of a band of frequencies occupied by the EKG signals.

Inventors: UNGER JOHN DAVID, UNGER, JOHN DAVID
Applicants: SIEMENS MEDICAL SYSTEMS INC, SIEMENS MEDICAL SYSTEMS, INC.
Application year: 1994
Main classification: A61B5
IPC codes: A61B5